Answer: Because the deal gave the insurance firm's disparate operations a common marketing theme as it relocated its global HQ to London in 2012 and increased awareness of the Aon brand in developing markets, especially Asia. Oh, and because there's nothing like bringing client prospects to watch the defending Premier League champions play at Old Trafford stadium.

The curious marketing relationship began in 2009 when Aon announced a $130 million, four-year deal to put its brand on the front of the club's jerseys.

"Aon had grown through something like 435 acquisitions at that point," said Phil Clement, Aon's global chief marketing and communications officer. "We were looking for one global platform we could promote that would bring the firm together."

It was also looking to grow in new regions, such as Asia. The company's brand awareness in Japan, for example, went from 0% to around 80%.

"Man U is particularly big in the Pacific Basin and China ... that name recognition goes way past where they're currently playing," said Tony Ponturo, Anheuser-Busch's former media chief.

Manchester United is the world's most valuable sports franchise with Forbe's valuing it at $1.86 billion. In April of last year, Aon signed a $230 million, eight-year extension with the club to put its brand on the club's training center in Northern England, plus practice uniforms and those worn in traveling exhibition games.

But it's losing real estate on the regular uniform. In a widely criticized deal, General Motors' former marketing czar Joel Ewanick agreed to pay $559 million over seven years to put Chevrolet's bowtie logo on the front of the jerseys.

While the first deal caused an "explosion" in awareness for Aon, Mr. Clement hopes this deal goes deeper. Seven years from now, he said, he hopes "we'll be able to see increases in the understanding of the Aon brand much like we saw the increases in the awareness."